In manufacturing tires, the actual shaping of the tire is caused by inflating a rubber bag inside a green tire carcass to force the tire into shape within the mold. Generally, there is substantial movement between the outer contact surface of the bladder, and the inner surface of the green tire during the expansion phase of the bladder prior to fully curing the tire. Likewise, there is considerable relative movement between the outer contact surface of the bladder and the cured inner surface of the tire after the tire has been molded and vulcanized during the collapse and the stripping of the bladder from the tire.
It is essential that there be sufficient lubrication between the bladder and the inner surface of the tire in order to reduce friction between the bladder and the inside of the raw tire and allows for optimum slip of the bladder during the shaping process when the raw tire and bladder are in friction with one another. In addition, the lubricant also serves to channel the trapped air and/or gasses during high temperature curing. Finally, at the termination of the vulcanization cycle, the lubricant allows for the release and removal of the bladder from inside the tire.
Aqueous organopolysiloxane emulsions containing treated inorganic silicates have been used as lubricants for molding tires. These emulsions are described in, for example, U.S. Pat. No. 4,184,880 to Huber et al in which an aqueous diorganopolysiloxane emulsion containing dispersed inorganic silicates which have been treated with organosilicon compounds to impart hydrophobic properties to the surfaces of the inorganic silicates have been employed as release agents for manufacturing tires. Also, U.S. Pat. No. 3,713,851 to Cekada describes aqueous organopolysiloxane emulsions which have been used as bag lubricants for molding tires in which the emulsion contains an alkyl methyl siloxane fluid including non-flowing gums, polyalkylene glycols, mica, carboxymethylcellulose, lecithin and water. U.S. Pat. No. 4,431,452 to Comper et al discloses a lubricating composition for a tire bladder comprising (1) a hydroxyl-terminated polydimethylsiloxane having a viscosity of up to about 25,000,000 centistokes at 25.degree. C., (2) a hydroxyl-terminated polydimethylsiloxane having a viscosity up to about 120,000 centistokes at 25.degree. C., (3) a polyalkylene glycol, (4) bentonite clay and (5) a surfactant. U.S. Pat. No. 3,872,038 to Adams et al discloses an aqueous emulsion which is useful as a bladder lubricant comprising (1) a silicone gum, (2) an organopolysiloxane fluid, (3) polyglycols, (4) mica, (5) lecithin, (6) sodium carboxymethylcellulose, (7) emulsifying agents and (8) water.
A bladder lubricant is described in U.S. Pat. No. 4,359,340 to Comper et al in which an aqueous emulsion comprising (1) a polydimethylsiloxane having a viscosity up to about 25,000,000 centistokes at 25.degree. C., (2) a methylhydrogen silane having a viscosity of from 20 to 40 centistokes at 25.degree. C., or a dimethylhydrogen silane having a viscosity of from 80 to 120 centistokes at 25.degree. C., (3) a metal salt of an organic acid and (4) surfactants is applied to the bladder surface.
An aqueous emulsion for treating organic fibers is described in U.S. Pat. No. 4,436,856 to Huhn et al in which the aqueous emulsion containing (1) an organopolysiloxane having at least two monovalent SiC-bonded organic radicals per molecule with a basic nitrogen atom, (2) an organopolysiloxane having at least 3 Si-bonded hydrogen atoms per molecule, (3) a catalyst for the condensation of Si-bonded condensable groups, (4) an emulsifier and (5) a diorganopolysiloxane containing an Si-bonded terminal hydroxyl group.
Aqueous organopolysiloxane emulsions employed heretofore as bladder lubricants in manufacturing tires have several disadvantages. For example, pre-formulated aqueous organopolysiloxane emulsions have stability problems in which the areas of ingredient settling, compaction and/or degradation during storage and/or during transportation, or upon inordinate changes such as freeze-thaw cycles that might be encountered.
In order to reduce the sliding friction and improve venting between the bladder and the inside of the tire, it has been necessary to increase the amount of filler or the amount of silicone polymer present in the composition and as the amount of filler increased, settling and compaction become a problem. In addition, many of the aqueous organopolysiloxane emulsions are not stable over long periods of time and have a tendency to "cream" and/or form an oil on the surface. Also, some of the organopolysiloxane emulsions contain catalysts which have a tendency to accelerate the degradation of the resultant emulsion and release hydrogen as a by-product. Furthermore, many of the aqueous organopolysiloxane emulsions have to be applied to the bladder just prior to shaping the tire, otherwise good lubricating properties and release properties are not achieved.
In contrast to the aqueous organopolysiloxane emulsions described heretofore, the aqueous organopolysiloxane emulsions of this invention are stable over long periods of time. Generally, the aqueous organopolysiloxane emulsions of this invention do not release hydrogen during storage. In addition, several tires can be manufactured with one application of the aqueous organopolysiloxane emulsions of this invention. Moreover, the aqueous organopolysiloxane emulsions of this invention can be applied to the inside of the green tire carcass and allowed to stand overnight without affecting the release properties. Furthermore, the inside of the green tire carcass can be coated with the aqueous organopolysiloxane emulsions away from the press area and then transferred to the press area where they are molded.
Therefore, it is an object of the present invention to provide an aqueous organopolysiloxane composition which may be used as a bladder lubricant. Another object of the present invention is to provide a composition which is stable over a long period of time. Another object of the present invention is to provide an aqueous organopolysiloxane emulsion which will give numerous releases per application. Still another object of the present invention is to provide an aqueous organopolysiloxane emulsion which may be applied to the inside of a green tire carcass several hours before the tire is molded. A further object of the present invention is to provide a method for preparing an aqueous organopolysiloxane emulsion. Still a further object of the present invention is to provide a method for molding tires using an aqueous organopolysiloxane emulsion.